Sensors are divided into several sub-categories to help you find what you are looking for:

Acceleration  Sensors that measure their own motion, i.e. accelerometers. This does not include devices that detect direction/tilt (see Orientation) or devices that passively detect movement in their surroundings (e.g. infrared motion sensors are in the Light category).

Pressure  Sensors that measure pressure, whether barometric (e.g. altimeters) or tactile forces like squeezing or weight. This does not include momentary touch sensors (see the Touch category) as those dont actually measure the force applied.

Touch  Devices that detect physical contact, e.g. capacitive touch sensors, fingerprint scanners, linear membrane potentiometers. This does not include devices that measure the amount of force applied when touched; see the Pressure category.

Magnetism/Current  Sensors that measure or react to levels of magnetism or current, e.g. Hall-effect sensors and reed switches. This does not include magnetometers used for direction sensing (see the Orientation category).

Flex/Stretch  Sensors that measure the amount of flexing or stretching applied to them.

Other  Any other type of sensor for which there wasnt enough selection to warrant its own category. Examples include dendrometers, soil moisture sensors, radiation sensors, inductive sensors, lightning detectors, and magnetic card readers (not RFID; see the RFID subcategory of our Wireless top-level category).

If youre planning on building a device with sensors, check out the Waspmote open-source wireless sensor networking platform.